In methods and arrangements for open-loop and/or closed-loop controlling an operating variable of an internal combustion engine, transfer elements are often used such as electrically actuable actuating elements which operate directly or indirectly on the operating variable to be open-loop or closed-loop controlled. The relationship between input and output variables or, with respect to the actuating element, between electrically driving variables and electrical operating variables or a variable influencing one of these operating variables is definable as a characteristic field or characteristic line. This relationship is fixed by means of such transfer elements. This characteristic field or this characteristic line is then subjected to influences which operate in a varying manner on the characteristic field or characteristic line so that the open-loop control and/or closed-loop control of the operating variable operates outside of its operating point provided during normal operation and sometimes at the periphery of its signal range. This can lead to a defective operation of the open-loop and/or closed-loop control which especially has negative effects on stability, precision and/or dynamic of the open-loop control and/or closed-loop control.
Influences of this kind can manifest, for example, with an actuator in a dependence of the actuator characteristic curve or actuator characteristic field on the temperature of the actuator winding. For a cold actuator, the winding of the actuator conducts a larger current than for a heated actuator for the same drive signal magnitude so that, for the same drive signal, a different value of the operating variable or of the variable influencing this operating variable is adjusted.
Battery voltage fluctuations have similar effects and, for an actuator controlling the air input, changes in the quantities of leakage air not influenceable by the actuator or changes of the ambient air pressure.
For this reason, measures for the adaptation of the trace of the actuator characteristic curve are provided in U.S. Pat. No. 4,672,934. This starts from an electromagnetic actuator having a pregiven characteristic curve which actuator is used for the air intake of the internal combustion engine for an idle engine speed control.
This adaptation undertakes a comparison between the desired value computed by the controller and the measured actual value of a variable influenced by the actuator and adjusts offset adaptation and slope adaptation independently of each other in dependence upon the comparison results in the operating branch of the characteristic curve which is the most linear. To avoid defective adaptations and for accelerating the adaptation procedure, release conditions are defined in U.S. Pat. No. 4,672,934 for the offset adaptation and slope adaptation which are related to each other.
The offset adaptation described there is however only capable of carrying out a correction of the characteristic curve at a single operating point. In operating states, wherein the influences on the actuator characteristic curve change rapidly, the course of the adaptation is therefore not satisfactory. In such an operating state, the offset adaptation, which is configured for rapid correction, operates continuously. This can lead to unsatisfactory running smoothness of the engine in this operating state. Only an intervention of the slope adaptation adapts the characteristic curve to the change circumstances and thereby quiets the adaptation operation and the running performance of the engine. The slope adaptation is subject to enabling conditions expanded because of function reasons since a repeated adaptation of the slope without adaptation of the base point can lead to defective functions of the open-loop control and/or closed-loop control system.
A transmission of the known actuator characteristic curve adaptation to pressure control systems (that is, systems which obtain the load information needed for determining the quantity of fuel to be metered on the basis of a signal representing the pressure in the intake pipe) is not possible. Especially in the transition from the part-load region into the idle state, a load value which is too high is determined from the pressure signal since the pressure signal supplies a correct load signal only after several work strokes. An adaptation carried out in this transition region would be defective and could possibly lead to unwanted operating conditions.
The invention therefore has the task to provide measures which improve the adaptation of the open-loop control or closed-loop control of an operating variable of an internal combustion engine to operating circumstances which change.
This is achieved by an adaptation of the characteristic field or the characteristic curve of the transfer element or of the actuator with at least one region of the characteristic field or the characteristic curve being rotated about a pregiven pivot point (A) specific to the actuator and lying outside of the characteristic field or the characteristic curve. The offset adaptation and slope adaptation known from the state of the art are carried out at the same time.
A further improvement of this characteristic field adaptation or characteristic curve adaptation is obtained in that a long-term adaptation of the pivot point (A) lying outside of the characteristic field or outside of the characteristic curve is undertaken for adaptation to conditions specific to the actuator.
One such actuator for controlling the throttle flap of an internal combustion engine in connection with an electronic accelerator pedal is known from U.S. Pat. No. 4,947,815.